Aluminum, multi-layer plastic sheets, etc. have heretofore been used as food packaging materials; they are molded by techniques such as stretch forming and thermoforming to produce food packaging containers. However, containers made of aluminum have disadvantages in that they are readily subject to breakage or deformation at a step of filling with contents or at transportation; in particular, such deformation leads to a serious reduction in product value since the deformed containers cannot be restored. Multi-layer plastic sheets include sheets made of polyolefins and polystyrenes. In addition, in order to increase the hygienic or decorative effect, materials with an aluminum-vacuum deposited layer laminated on the surface thereof have been proposed. Although these laminated materials are sufficiently applicable for use as packaging materials, they suffer from disadvantages in that in the producing of various containers the surface becomes uneven and is readily scratched, and there cannot be obtained the decorative effect of the luster of aluminum. Furthermore, they are inferior in respect of gas barrier properties, light-shielding properties, heat resistance, and so forth. Another type of laminated material which has been proposed is produced by laminating a multilayer consisting of a metal-vacuum deposited layer as an inner layer and a thermoplastic resin sheet as an outer layer on a soft type resin such as low density polyethylene by an extrusion lamination process. These materials, when produced in combination with sheets having high rigidity, suffer from disadvantages in that when they are treated under high temperature sterilizing conditions, the metal-vacuum deposited layer is broken up, and they become unsuitable for practical use. Thus, they are limited in their utilization.